Apparatus including a steam generator and method of controlling the same

ABSTRACT

Steam-generating apparatus ( 1 ) and method for controlling same, wherein said steam-generating apparatus ( 1 ) comprises a water reservoir ( 5 ), a boiler ( 6 ) for generating steam, a sensor ( 14 ) connected to the boiler ( 6 ) for detecting the temperature of or pressure in the boiler ( 6 ), a pump ( 7 ) configured to pump water from the reservoir ( 5 ) to the boiler ( 6 ), and a controller ( 15 ) configured to receive a signal from the sensor ( 14 ) and to control operation of the pump ( 7 ) in dependence on said signal, the controller ( 15 ) is configured to determine an amount of water within the boiler ( 6 ) and to control the pump ( 7 ) to supply water to the boiler ( 6 ) when the determined amount of water is less than a predetermined value; moreover, said controller ( 15 ) is arranged to determine the amount of water by measuring at least one time interval needed for predetermined increase in temperature or pressure of the boiler ( 6 ) and to compare the measured time interval with a predetermined value.

TECHNICAL FIELD

The present invention relates to an apparatus that includes a steam generator, such as an iron for clothing, and in particular, to such an apparatus having improved control of a steam generator, and a method of controlling such an apparatus.

BACKGROUND OF THE INVENTION

Appliances such as clothes irons, garment steamers and steam cleaners include a steam generator system having a boiler to convert water into steam which in turn is supplied to the soleplate of the iron and exits onto the clothing being ironed through steam vents in the soleplate. As water is turned into steam in the boiler and vented out of the appliance, the water level in the boiler reduces and so a water feed to boiler is required. A pump may be used to pump water from a water reservoir within the appliance to the boiler. The pump may be automatically controlled so as to feed sufficient water to the boiler when required. To achieve this function, accurate and precise sensing of water level in the boiler is required to generate a control signal for the pump. This may be done by directly measuring the water level in the boiler or indirectly by measuring water temperature or pressure in the boiler.

Direct boiler water level measurement is often more complicated and expensive to manufacture due to the requirement to integrate a sensor within the boiler and also the requirement to electrically isolate the sensor. In addition direct water level measurement has a disadvantage that scale can form on the surface of sensor over time which deteriorates the sensing accuracy.

Indirect boiler water level measurement is often simpler to implement but can be less accurate since determination of the water level is often based on extrapolation of temperature or pressure changes plotted from limited data measurement points. EP 0843039 discloses an appliance having a steam generator that utilises indirect boiler measurement and such extrapolation of temperature or pressure changes. In this disclosure, the water level is determined by measuring a temperature drop of a boiler over a predetermined time period during steam release from the boiler. However, in this disclosure, and in other devices that utilise such a water-level determination process, the temperature drop while the steam outlet valve is open is affected by many factors, including the valve opening diameter, steam hose length between the boiler and steam outlet vent, number of steam outlet vents in the appliance, the variable back pressure on steam outlets at time of use (for example, due to steam outlet path variation due to bending or coiling of the steam outlet hose and/or vents of an iron soleplate being covered by a garment), the peak pressure achieved in the boiler at the point of valve opening, and the effects of voltage amplitude applied to the heater slowing down the rate of cooling of the boiler during steam release. Therefore, the actual line of temperature drop against time of the boiler during the steam release is curved or significantly varying in gradient over the period of steam release. This means that measurement of a small number of points and extrapolation of a straight line from those few points on such a varying and/or curved plot will render the calculation of water level within the boiler inaccurate. This also means that the rate of temperature drop during steam release is not constant for a given volume of water in the boiler.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an apparatus including a steam generator, and a method of controlling the same, which substantially alleviates or overcomes the problems mentioned above.

The invention is defined by the independent claims; the dependent claims define advantageous embodiments.

One aspect of the invention provides a steam-generating apparatus comprising a water reservoir, a boiler for generating steam, a temperature or pressure sensor connected to the boiler for detecting the temperature or pressure of the boiler, a pump configured to pump water from the reservoir to the boiler, and a controller configured to receive a signal from the sensor and to control operation of the pump in dependence on the signal, wherein the controller is configured to determine an amount of water within the boiler and to control the pump to supply water to the boiler when the determined amount of water is less than a predetermined value, characterised in that the controller is arranged to determine the amount of water by measuring at least one time interval needed for a predetermined increase in temperature or pressure of the boiler and to compare the measured time interval with a predetermined value.

The predetermined time value may correspond to a time interval for one or more known amounts of water to reach the predetermined increase in temperature or pressure.

The apparatus may further comprise a control valve to allow steam to be released from the boiler, wherein the controller may be configured to measure a time interval for an incremental increase in boiler temperature or pressure only when the control valve is closed and steam is prevented from being released from the boiler. This ensures time interval(s) are measured in a condition when steam is not being expelled from the boiler for consistent and accurate prediction and extrapolation of increasing temperature rate. This also ensures a more stable boiler condition and more consistently repeatable temperature of pressure measurement results, and avoids the problems of known water-level detection methods and devices mentioned above.

The controller may be configured to start measurement of a time interval for an incremental increase in boiler temperature or pressure following closing of the control valve after steam has been released from the boiler, and after a predetermined time period has elapsed after closure of the control valve. The predetermined time period may be dependent on the time period for which the control valve has been opened. Such a predetermined time period may comprise around 1-5 seconds. This advantageously allows for the thermal inertia in the system and response time of the sensor after the end of the previous steam expulsion event. This allows the system to settle to a steady thermal state before commencing the process described above.

The controller may be configured to start measurement of a time interval for an incremental increase in boiler temperature or pressure following closing of the control valve, and once a detected temperature or pressure within the boiler reaches a threshold value. This advantageously allows the temperature and/or pressure within the boiler to stabilise before measurements begin to be taken, allowing for more accurate and reliable measurements. The threshold at which measurement commences may be a threshold temperature, and may be a threshold at or above the boiling point of water, and may be 120° C., or may be 123° C.

The controller may be configured to operate the pump when the or each measured time interval for an incremental increase in temperature or pressure of the boiler is less than a predetermined time interval. This advantageously indicates when more water is required in the boiler if the water level in the boiler is below a predetermined minimum volume, since a smaller volume of water would heat quicker than a predetermined threshold time interval.

The controller may be configured to operate the pump for a predetermined period of time. The predetermined period of time may be fixed, or may be dependent upon the determined amount of water remaining in the boiler. A fixed pump time results in a simpler control method, although determining the volume of water to be pumped based on the measured remaining amount allows for a more accurate control of the water level within the boiler.

The controller may be configured to measure the or each time interval for an incremental increase in boiler temperature or pressure during or after an operation of the pump. The determined water level during or after an operation of the pump may be used to determine the next operation of the pump.

The controller may be configured to stop the pump if the determined water level does not increase in accordance to the period of time of pump operation. This advantageously helps towards preventing continuous pumping when the water reservoir is depleted and the potential damage to the pump.

The controller may comprise a microprocessor and one or more memory units. The predetermined value may comprise a time interval for incremental temperature or pressure increases of one or more known amounts of water within the boiler may be stored in one or more look-up tables within a memory unit of the controller. These enable a quick reference for the controller to determine the measured time intervals for incremental temperature increases against that for known volume(s) of water in the boiler.

The controller may further be arranged to control operation of the boiler in dependence upon a temperature or pressure signal from the sensor and may stop the boiler heating water when the sensed temperature or pressure reaches a predetermined threshold value. This advantageously helps towards preventing overheating of the boiler with associated over-pressure consequences and potential damage to the apparatus.

The sensor may comprise a temperature sensor, and may comprise a thermistor, and may comprise a negative temperature coefficient (NTC) thermistor. The thermistor may be mounted to a metallic substrate and the metallic substrate may be mounted to the boiler. The sensor may be mounted to a top or upper portion of the boiler. The sensor may be mounted to an outer surface of the boiler. This advantageously avoids deterioration of the sensor through calcification.

The apparatus may comprise more than two temperature sensors which may comprise thermistors as described above. Each sensor may be mounted to an upper or top portion of the boiler, or one may be mounted to an upper or top portion and another may be mounted to an alternative portion of the boiler. This advantageously enables accurate temperature measurement by at least one sensor being spaced apart from the heater element so as not to detect directly the heater temperature. Placing the temperature sensors in a spaced relationship advantageously allows determination of accurate temperature measurement by enabling comparison of temperatures detected at different points in the boiler. It also advantageously allows detection of a dry boiler condition, if one sensor is placed proximate the heater, by detecting an excessive heating of the boiler in the absence of water, or by detecting an excessive difference between temperatures sensed by a sensor proximate the heater and a sensor remote from the heater. The sensor proximate the heater may comprise a cut-off device such as a thermostat.

Alternatively, the or each sensor may comprise a pressure sensor. In a closed volume boiler of known dimensions, temperature and pressure are well correlated and so may be functionally interchangeable.

There is also disclosed herein a method of operating a steam generating apparatus which comprises a water reservoir, a boiler for generating steam, a temperature or pressure sensor connected to the boiler for detecting the temperature of or pressure in the boiler, a pump configured to pump water from the reservoir to the boiler, and a controller configured to receive a signal from the sensor and control operation of the pump in dependence on the signal, the method comprising determining an amount of water within the boiler and controlling the pump to supply water to the boiler when the determined amount of water is less than a predetermined value, characterised in that the method comprises determining the amount of water by measuring at least one time interval for a predetermined increase in temperature of or pressure in the boiler and comparing the measured time interval with a predetermined value.

The method may comprise measuring a time interval for an incremental increase in boiler temperature or pressure only when a control valve to allow steam to be released from the boiler is closed and steam is prevented from being released from the boiler.

The method may comprise starting measurement of time interval for an incremental increase in boiler temperature or pressure following closing of the control valve after steam has been released from the boiler, and after a predetermined time period has elapsed after closure of the control valve. Such predetermined time period may comprise 1-5 seconds, any may comprise around 3 seconds.

The method may comprise operating the pump for a predetermined period of time in dependence upon the determined amount of water remaining in the boiler.

The step of comparing the measured time interval with a predetermined value may comprise comparing a measured time interval with a predetermined time interval for an incremental temperature or pressure increase of one or more known amounts of water within the boiler stored in one or more look-up tables within a memory unit of the controller.

The method may comprise controlling operation of the boiler in dependence upon a temperature or pressure signal from the sensor and stopping the boiler heating water when the sensed temperature or pressure reaches a predetermined threshold value. This prevents overheating of the boiler and/or excessive pressure build-up within the boiler.

The controller may be configured to perform measurement of one or more time intervals for incremental increases in temperature or pressure of the boiler within a predetermined range of temperatures or pressures of the boiler. Such range of temperatures may comprise from 120° C. to 160° C., or may comprise from 123° C. to 146° C. The boiler may be configured such that the range of temperatures over which the controller performs measurement of the time interval(s) for one or more incremental increases in temperature of the boiler corresponds to a predetermined range of internal pressure of the boiler. Such predetermined range of internal pressure of the boiler may comprise between 1.5 Bar and 6.5 Bar.

The water reservoir of the apparatus may be unpressurised. A one-way valve may be provided between the pump and the boiler to prevent steam passing back to the pump and/or the reservoir. This advantageously prevents inaccurate boiler control which would result from escaping steam during a measurement process, and also avoids pump damage by preventing exposure to steam.

The increments of increasing temperature over which time intervals are measured may comprise constant temperature increments over the measurement range, and may comprise increments of one degree Celsius, although the invention is not intended to be limited to single degree Celsius increments.

The boiler may comprise one or more heating elements. The heating element(s) of the boiler may be internal or external to the boiler. Internal elements may more efficiently heat the water within the boiler, although external elements are advantageous in avoiding deterioration such as calcification by the boiling of the water.

The controller may be configured to continue measuring one or more time intervals for predetermined incremental increases in temperature or pressure of the boiler during a heating operation of the boiler and comparing the measured time intervals with predetermined time intervals for incremental temperature or pressure increases of one or more known amounts of water within the boiler until an upper threshold temperature or pressure of the boiler is reached or an actuator or trigger operating the control valve is operated to release steam from the boiler.

The controller may be configured to perform the or each measurement of time interval(s) for predetermined incremental increase(s) in temperature or pressure of the boiler and compare the measured time interval(s) with known time interval(s) for incremental temperature or pressure increase(s) of known water levels, during the period when the sensed temperature or pressure in the boiler is below the predetermined threshold temperature or pressure and power is being supplied to the boiler.

The apparatus may comprise an actuator button or trigger operable to actuate the control valve. The controller may be connected to the control valve and/or the actuator button to detect actuation of the control valve and/or the actuator button.

The apparatus may comprise a clothes steam iron appliance, and may comprise a base portion and a hand-held portion. The hand held portion may be electrically and fluidly connected to the base portion for the supply of power and steam from the base portion to the hand-help portion. The reservoir, pump and boiler may be provided in the base portion. An actuator button may be provided on the hand-held portion operable to actuate the control valve.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of an appliance according to a first embodiment of the invention;

FIG. 2 shows a graph with a plot of boiler temperature versus time for a given volume of water within the boiler;

FIG. 3 shows a graph with multiple plots of temperature versus time for a range of volumes of water within the boiler

FIG. 4 shows a first exemplary look-up table of the controller of the appliance of the invention;

FIG. 5 shows a flow chart illustrating the method of operation of the invention; and

FIG. 6 shows a second exemplary look-up table of the controller of the appliance of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to FIG. 1, an appliance of a first embodiment of the invention is schematically shown, which in this exemplary embodiment, comprises a steam iron 1. The steam iron 1 includes a body 2 and a soleplate 3. The steam iron 1 is configured to apply steam to clothes being ironed through apertures 4 in the soleplate 3.

The steam iron 1 includes a water reservoir 5 and a boiler 6. A pump 7 is provided to pump water from the reservoir 5 to the boiler 6. A first conduit 8 fluidly connects the reservoir 5 to the pump 7, and a second conduit 9 fluidly connects the pump to the boiler 6. The reservoir 5 is an unpressurised container. The boiler 6 comprises a closed container or shell, with a heating element 10 to heat water within the boiler 6 to make steam. The heating element is shown disposed within the boiler 6 although may equally be disposed on an outer surface of the boiler shell within the scope of the invention. A third conduit 11 connects the boiler 6 to the body 2 of the steam iron 1 for the supply of steam from the boiler 6 to the body 2 of the steam iron 1 to be expelled from the apertures 4 in the soleplate 3.

A control valve 12 is provided to control the supply of steam from the boiler 6 to the soleplate 3. This may be provided in the third conduit as shown in FIG. 1, or may alternatively be provided in the body 2 of the iron 1, or alternatively also on the body 6 of the boiler. The body 2 of the iron includes an actuator 13 which operates the control valve 12. A user can thereby control steam to be expelled through the soleplate 3 by pressing the actuator 13.

The boiler 6 includes a sensor 14 on an upper surface of the boiler shell which, in this first embodiment comprises a temperature sensor. However, as will be described later, the invention is not intended to be limited to use of a temperature sensor and alternatively, a pressure sensor may be provided within the scope of the invention. The temperature sensor 14 is preferably a NTC thermistor which is secured to the boiler shell, for example by being bonded thereto, and is in good thermal contact with the boiler shell. Advantageously, the thermistor is mounted to a metallic substrate (not shown) which is itself mounted to the boiler shell. This provides very good thermal conductivity between the boiler shell and the thermistor and reduces the thermal inertia and delay in response of the thermistor. The temperature sensor being mounted on an upper surface of the boiler shell is advantageous because it means more consistent temperature readings are obtained relating to steam temperature within the boiler. If the temperature sensor 14 was on the bottom of the shell, for example, a significant drop in temperature of the boiler shell would be detected whenever cool water is pumped into the boiler 6 from the reservoir 5, distorting the indication of the amount and temperature of steam remaining within the boiler 6.

A controller 15 is provided to control operation of the steam iron 1 and includes a microprocessor and a memory unit. The controller 15 is connected to the heater 10 and to the pump 7 to control operation of these two components. The controller 15 is connected to the temperature sensor 14 to receive temperature signals from the temperature sensor 14. The controller 15 is also connected to the control valve 12 to determine when the control valve 12 is on or off, as determined by a user by operation of the actuator 13.

The steam iron 1 is connectable to an external power supply, such as domestic mains electricity, by a power cable (not shown), to power the various components of the iron 1, including the heating element 10 of the boiler 6, heating element(s) in the soleplate 3 (not shown), the pump 7 and the controller 15.

The controller 15 is configured to control operation of the pump 7 to supply water from the reservoir 5 to the boiler 6 when the water level in the boiler is low, in dependence upon temperature signals received from the sensor 14. More specifically, the controller determines an unknown remaining volume of water in the boiler 6 by measuring the rate of increase in temperature of the boiler during a period when the actuator 13 is not operated and therefore steam is not being expelled by the steam iron 1. The controller determines time intervals taken for the sensed temperature of the boiler to increase in pre-determined temperature increments when the heater 10 is activated. The controller 15 then compares these measured time values against known time intervals, which are stored in the memory of the controller 15, for given volumes of water in the boiler 6 and uses this comparison of the measured time values against known time values to determine whether the volume of water remaining in the boiler 6 is below a minimum threshold value at which the boiler 6 needs to be refilled. If refilling is required, the controller 15 operates the pump 7 for an appropriate period to refill the boiler 6 with a required volume of water.

In embodiments of the invention, the controller measures the time taken for each degree Celsius rise in sensed temperature of the boiler 6. These measurements may occur within a predetermined range of temperatures of the boiler 6, for example, between 120° C. and 160° C., which may correspond to an internal pressure within the boiler 6 of between 1.5 Bar and 6.5 Bar. The time measurements for increasing temperature are taken when the control valve 12 is closed and so no steam may escape or be expelled from the boiler 6.

Since the volume of the boiler is constant, the power supplied to the boiler (e.g. from the mains voltage) is constant, and the control valve 12 is closed during the measurement process, the only variable factor that can affect the rate at which the water temperature within the boiler increases is the mass of water within the boiler 6. As such, for a given boiler 6 and power input, accurate predetermined values of time taken for incremental increases in temperature for specific volumes of water can be calculated. Plots of such known time intervals for incremental temperature increases are shown in FIGS. 2 and 3. FIG. 2 shows a graph plot of time (y-axis) in seconds against increasing temperature increments (x-axis) in degrees Celsius for a given volume of water (e.g. 350 ml) being heated in the boiler 6. This is shown as the single line i in FIG. 2. FIG. 3 shows groups of plots of temperature increments against time, each group comprising three test plots for different volumes of water in a boiler. The graph of FIG. 3 comprises plots for 350 ml (group A comprising lines i, ii and iii), 300 ml (group B comprising lines iv, v and vi), 250 ml (group C comprising lines vii, viii and ix) and 200 ml (group D comprising lines x, xi and xii) of water in a boiler. This data relating to the rising linear plot lines for known volumes of water are stored as reference data in look-up tables in the memory of the controller 15, as shown in FIG. 4. The exemplary look up table in FIG. 4 shows data within the temperature range mentioned above, namely a start temperature T_(emp) of 120° C. and an end temperature T_(emp) of 160° C. In between these start and end temperature values are incrementally increasing temperature values. These are not shown in FIG. 4. Instead, one pointer temperature value T_(ptr) is shown in FIG. 4, which is relevant for the control process of the invention as will be explained in more detail below. Against each temperature value are time values in seconds for the respective volume of water in the boiler to reach each incremental temperature value. The time values start from zero at the start temperature. In FIG. 4, the time at the end temperature value is simply shown as ‘n’ as this will differ for each look-up table that relates to different volumes of water.

It can be seen from the plots in FIG. 3 that, as would be expected, the plots for 200 ml of water (group D) take less time to increase in temperature (by being shallower plot gradient) than the plot lines for 250 ml (group C), which in turn are shallower than the plot lines for 300 ml (group B), which again are shallower than the plot lines for 350 ml (group A) of water.

Referring to FIG. 5, a logic process of the controller 15 of the invention is shown as a flow chart. Since the time measurement of the control process of the invention occurs when the control valve 12 is closed (i.e. when no steam may be expelled through the sole plate 3), the process begins from a start point at S0 and comprises a first step S1 at which the controller 15 determines whether the electronic control valve 12 is closed. If not, the process loops back to before step S1 until it is determined that the control valve 12 is closed. If it is determined at step S1 that the control valve is closed, the process proceeds to step S2.

At step S2, the temperature T_(emp) of the boiler 6 sensed by the sensor 14 is measured. The process then proceeds to step S3, in which the controller determines whether the measured temperature T_(emp) is greater than a value of a pointer temperature minus 1 (T_(ptr)−1) and less than a value of a pointer temperature plus 1 (T_(ptr)+1). The control operator for this step can be represented as [(T_(ptr)−1)<T_(emp)<(T_(ptr)+1)]. Here, the pointer temperature T_(ptr) is the incremental increasing temperature along the x-axis against which time measurements are to be recorded, and this value is initially set at a value at the lower end of the range within which temperature measurements are to be taken, for example 120° C. If the measured temperature T_(emp) is within the range (T_(ptr)−1) and (T_(ptr)+1), then the process proceeds to step S4 at which a time measurement t at that moment, counting from the start of the measurement process, is captured. If the measured temperature T_(emp) is not within the range (T_(ptr)−1) and (T_(ptr)+1), then process proceeds to step S5 at which the pointer temperature T_(ptr) is incremented by one degree. The process then loops back to step S2 to detect the boiler 6 temperature again.

After step S4, at step S6 the controller 15 determines from the look-up tables whether the measured time t is less than a reference time in the look-up table for the pointer temperature value in question (t@T_(ptr)) at a threshold volume of water below which refilling is required. This control operator can be represented as [t<t@T_(ptr)?]. If yes—namely the water in the boiler 6 has heated up quicker than a time interval for a minimum threshold volume of water, then the volume of water within the boiler 6 is below the threshold volume and the process proceeds to step S7 at which the controller 15 activates the pump 7 for a predetermined period of time to refill the boiler 6 with water, after which the process loops back to the beginning to repeat from step S1. The period of time the pump 7 operates to refill the boiler 6 is predetermined based on the known boiler volume and the threshold minimum volume at which the pump activates, and the known pump specification including the pump's fluid flow rate.

If the controller determines at step S6 that the measured time t is greater than a reference time in the look-up table for the pointer temperature value in question at a threshold volume of water below which refilling is required, then it is not necessary to fill the boiler 6 with more water and so the process loops back to the beginning to repeat from step S1. The process then continues as described above to record the time intervals for incremental temperature increases as the water in the boiler 6 continues to heat up.

The temperature in the boiler 6 is regulated to remain below an upper threshold value. The controller 15 receives temperature signals from the sensor 14 and if the sensed temperature reaches the upper threshold value, the controller 15 turns off the heater 10 of the boiler 6. It will be appreciated that the above-described process occurs whilst the heater 10 is activated and is heating water in the boiler, and the control valve 12 is closed. Therefore, steps S2 to S7 of the above control process is repeated until the threshold temperature is reached (and the heater 10 is then turned off by the controller 15) or the actuator 13 is operated by the user (and the control valve 12 is thereby opened to expel steam). Thereafter, the whole process is repeated upon every release of the actuator 13—i.e. after each steam expulsion event.

In an embodiment of the invention, the controller 15 advantageously includes a delay time t_(d) (not shown in the Figs.) after step S1 after a positive response is obtained, before taking a temperature measurement T_(emp) in step S2. This delay t_(d) corresponds to a time delay from the moment the actuator 13 is released by a user and the control valve 12 closes, stopping expulsion of steam from the boiler 6 through the apertures 4 in the soleplate 3. This delay allows for the thermal inertia in the system and response time of the sensor 14 after the end of the previous steam expulsion event. This allows the system to settle to a steady thermal state before commencing the process described above. Such a delay period t_(d) may vary within the scope of the invention but advantageously may be around 1-5 seconds, and may be around 3 seconds. In such an embodiment, the above-described control process is repeated upon every release of the actuator 13 if the period after operation of the actuator exceeds the predetermined delay time t_(d).

It can be seen from FIGS. 2 and 3 that the rising temperature vs. time plots are substantially linear and so it is possible to accurately calculate the rising gradient of the graph plot from only a few closely spaced temperature increment/time measurements (e.g. one degree Celsius increments), and to accurately predetermine time intervals taken for a given volume of water to heat up by given temperature increments for a known boiler specification and power supply by extrapolation from those measurements. The linear plots are related to, and represent, the heat capacity and specific heat of water within the closed environment of the boiler 6 (since time measurements are taken when the steam outlet valve is closed), and for a given (constant) volume of water. The linearity is thereby related to these constant factors which enable the accurate and predictable water volume prediction of the method and apparatus of the invention. It also means that it is not critical at what boiler temperature, within a measurement range, the time interval measurement process is commenced because the plot line of time vs. temperature, and the rate of water heating within the boiler, is substantially linear across the temperature range either side of the process start point temperature. This linearity of plot lines makes the method of volume determination of the invention significantly more accurate than other methods where, for example, decreasing temperature or pressure measurements of a boiler of a steam generation device are taken over a time during which steam is being expelled from the boiler. This is because a plot of temperature decrease during steam expulsion against time is much less linear and is more curved/parabolic, meaning extrapolation from a few closely spaced initial measurements is inaccurate. Also, temperature decrease during steam expulsion is affected by a number of variables, such as back pressure on the soleplate due to garments covering the steam apertures, peak pressure and temperature within the boiler at the point when the valve is opened to commence steam expulsion and the degree of valve opening diameter/size. Therefore, such variables make predictions of water volume within a boiler based on measured temperature or pressure decrease during steam expulsion inaccurate.

The use of look-up tables in the apparatus and method of the invention compensates for any slight non-linearity that may exist in the actual rising time vs. temperature plot line. Also, the method and apparatus of the invention is not affected by variables in other processes or systems such as those mentioned above. The use of look-up tables also means that different power supply voltages, for example different mains voltages in different countries, can easily be accounted for by including in the controller memory further pre-programmed time interval and temperature increment data for a given boiler specification for known volumes of water, for different power supplies. The controller can then reference the relevant look up table data in dependence upon the detected power supply voltage being used with the appliance.

The embodiment of the invention described above may comprise a clothes steam iron appliance in which the water reservoir 5, pump 7 and boiler 6 are provided within a fixed base and the body 2 of the iron and soleplate 3 are a handheld component of the overall appliance. In such an embodiment, the base would be connected to the mains power supply and the iron body 2 would be connected to the base by a steam supply duct to supply steam from the boiler 6 to the soleplate 3, and an electrical power cable for the supply of power from the base to the heating elements within the soleplate. The actuator 13 would be provided on the body 2, although the control valve 12 may be either within the body 2 or within the base.

In an alternative embodiment of the invention, the controller 15 may be configured such that at step S3, if it is determined that the measured temperature T_(emp) is between (T_(ptr)−1) and (T_(ptr)+1), at step S4, the controller 15 sets the timing counter to zero (i.e. t=0) and then begins timing the time taken for a predetermined incremental temperature increase (e.g. one degree Celsius) above T_(ptr) to occur. That is, the control system loops around taking temperature T_(emp) measurements until the measured temperature T_(emp) reaches the predetermined incremental temperature increase above T_(ptr). Once that temperature increase has been achieved, the time t is captured for achieving that increase. Then, the controller 15 may use the measured time t to reference a relevant look-up table for the particular T_(ptr) value and compare if the measured time t is higher or lower than a reference time in the look-up table, in step S6. Such a look-up table is shown, as an example only, in FIG. 6, and may store different time period values to heat a range of volumes of water (e.g. 50 ml, 100 ml, 150 ml, 200 ml . . . etc.) by an incremental temperature increase from a given T_(ptr) temperature (shown as T_(ptr)=135 degrees Celsius in the table of FIG. 6). If, for example, the measure t is 6.2 seconds, then the controller 15 will determine, using the exemplary look-up table of FIG. 6, that the water level in the boiler 6 is between 150-200 ml. Based on the target water level to be maintained in the boiler 6 (which may be preset in the controller or operating program instructions), the controller 15 will make a decision at step S6 whether or not to activate the pump 7, and if yes, for how long. (For example, if target water level is 250 ml, then controller may operate the pump for 3 seconds). In one mode of operation of the invention, the pump 7 may have only one fixed time interval of operation. However, within the scope of the invention, the pump 7 may have a variable mode of operation, for example, variable pumping time which may be based on the difference between estimated water level and a target water level, and the controller 15 may then operate the pump 7 for a required period of time depending on how much water it is determined is required to fill the boiler 6 to the pre-determined level.

In an alternative operation of the embodiments described above, at step S6 the controller 15 may compare the measured time t with time values of a plurality of stored look-up table time values at the corresponding pointer temperature T_(ptr) (t@T_(ptr)) for a range of known volumes of water, instead of only determining whether the measured time t is less than a reference time for the pointer temperature value at a threshold minimum volume of water below which refilling is required. In this alternative embodiment, the controller can determine the actual volume of water within the boiler 6, not just whether volume of water within the boiler is below a minimum value for refilling. Therefore, once the actual volume of water remaining within the boiler has been determined, the controller 15 can determine the volume of water needed to be pumped into the boiler 6 to fill the boiler 6, and therefore can operate the pump 7 for an appropriate amount of time to fill the boiler 6. The period of time the pump 7 operates to refill the boiler 6 would be predetermined based on the known total boiler volume and the various known volumes relating to each look up table, and the known pump specification including the pump's fluid flow rate.

In an embodiment of the invention, the controller may be configured to measure the time intervals for incremental increases in boiler temperature during or after operation of the pump in order to provide more accurate water level control within the boiler. In such an embodiment, the controller performs an iterative loop of time measurements as part of the method of operation. As such, referring to FIG. 5, rather than just performing one measurement of time for a temperature increase for each time the control valve 12 is closed, the process loop may instead loop back from step S7 where the pump is activated, to step S2 to repeat the temperature and time measurement process.

In such an alternative apparatus and method of the invention, the controller may be configured to detect when the reservoir 5 is empty, by measuring a temperature before and after a pump activation step at S7. If there is no change (or an increase) in the sensed temperature within the boiler, it indicates that no water was fed by the pump 7 from the reservoir 5 to the boiler because the reservoir is empty and so the water level within the boiler has not increased. In order to prevent continuous operation of the pump when the reservoir is empty (which could damage or cause excessive wear to the pump), the controller 15 may be configured to stop the pump if it is determined that the water level within the boiler does not increase after an operation of the pump, indicated by no detected change (or an increase) in boiler temperature after operation of the pump.

In addition to the above, in such an alternative apparatus and method of the invention, by measurement of time intervals for incremental increases in boiler temperature during or after operation of the pump, the controller is able to determine the water level within the boiler and may therefore store in a memory of the controller the current water level. This may then be used to determine the next operation of the pump, in terms of when to next refill the boiler, or the duration of pump operation required at the next pump operation to fill the boiler with the required amount of water.

In the embodiment described above, a single sensor 14 is provided on shell of the boiler 6. However, in an alternative embodiment of the invention, two temperature sensors may be provided on the boiler shell. These may both be placed on different portions of the upper surface of the boiler shell and the controller 15 may receive signals from both sensors and average the two values to obtain more accurate readings of the boiler temperature. Alternatively, one sensor may be mounted on the top of the boiler shell and another may be mounted on a side wall of the boiler shell. Again, the controller 15 may receive signals from both sensors and average the two values to obtain more accurate readings of the boiler temperature.

In a dry boiler condition (i.e. in the absence of water in the boiler), no steam can be generated and therefore the sensor will not be measuring the steam temperature and instead would be measuring the boiler shell temperature. The use of two sensors may be used to detect a dry-boiler condition and prevent overheating. In such a case, a first sensor is positioned away from the heater 10, preferably on the top of the boiler shell, so as not to be affected by the heater temperature, and is used for measuring the temperature of the steam inside the boiler. The first sensor (14, as in FIG. 1) is therefore not sensitive to the temperature of the heater at the bottom. A second sensor (not shown) may be provided at or near the bottom of the boiler so that it can detect any overheating at the bottom. In such an embodiment, second sensor may be a cut-off device such as a thermostat, which may enable the heater 10 to be stopped if the detected temperature at the location of the second sensor exceeds a predetermined value (indicative of the heater 10 heating to a high temperature in the absence of water). Alternatively, the controller may be configured to compare the sensed temperatures of the first and second sensors and, if the difference between the two values is above a predetermined value, it indicates a dry-boiler condition. This is because the heater would heat to a high temperature in the absence of water and be detected by the second sensor, and the absence of steam would mean the first sensor would not be exposed to any heated steam so would detect a lower temperature than expected. In such a situation, the controller may be configured to stop operation of the heater 10 to avoid damage to the apparatus.

In the embodiments described above, the sensor 14 comprises a temperature sensor. However, it is intended with the scope of the invention that the sensor may alternatively comprise a pressure sensor. In a closed boiler system such as that of the embodiments described above, temperature and pressure are well correlated and so may be functionally interchangeable. In such an alternative embodiment, operation of the apparatus would be as described above except that where a sensor signal relating to a measured temperature is stated, this is to be replaced with a sensor signal relating to pressure within the boiler. The time measurements may be taken within a range of boiler pressures, such as between 1.5-6.5 Bar, as mentioned above, and the look-up table, such as that shown in FIG. 4, may store known time intervals taken to reach predetermined boiler pressures within such a range for known volume(s) of water. Such an alternative apparatus and method of operating such an apparatus would still provide the above-described advantages over known systems.

Although the embodiment of the invention described above is a steam iron 1, the invention is not intended to be limited to such an appliance and may comprise other forms of steam generating device, for example, clothes steamers, wall-paper steamers, steam ovens, or steam cleaning devices e.g. for cleaning floors.

It will be appreciated that the term “comprising” does not exclude other elements or steps and that the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to an advantage. Any reference signs in the claims should not be construed as limiting the scope of the claims. 

1. A steam-generating apparatus comprising a water reservoir, a boiler for generating steam, a sensor connected to the boiler for detecting the temperature of or pressure in the boiler, a pump configured to pump water from the reservoir to the boiler, and a controller configured to receive a signal from the sensor and to control operation of the pump in dependence on the signal, wherein the controller is configured to determine an amount of water within the boiler and to control the pump to supply water to the boiler when the determined amount of water is less than a predetermined value, wherein the controller is arranged to determine the amount of water by measuring at least one time interval needed for a predetermined increase in temperature of or pressure in the boiler and to compare the measured time interval with a predetermined value.
 2. A steam-generating apparatus according to claim 1 wherein the predetermined time value corresponds to a time interval for one or more known amounts of water to reach the predetermined increase in temperature or pressure.
 3. A steam-generating apparatus according to claim 1 further comprising a control valve to allow steam to be released from the boiler, wherein the controller is configured to measure a time interval for an incremental increase in boiler temperature or pressure only when the control valve is closed and steam is prevented from being released from the boiler.
 4. A steam-generating apparatus according to claim 3 wherein the controller is configured to start measurement of a time interval for an incremental increase in boiler temperature or pressure following closing of the control valve after steam has been released from the boiler, and after a predetermined time period has elapsed after closure of the control valve.
 5. A steam-generating apparatus according to claim 1 wherein the controller is configured to operate the pump when the measured time interval for an incremental increase in temperature or pressure of the boiler is less than a predetermined time interval.
 6. A steam-generating apparatus according to claim 1 wherein the controller is configured to operate the pump for a predetermined period of time in dependence upon the determined amount of water remaining in the boiler.
 7. A steam-generating apparatus according to claim 1 wherein the predetermined value comprises a time interval for an incremental temperature or pressure increase of one or more known amounts of water within the boiler which are stored in one or more look-up tables within a memory unit of the controller.
 8. A steam-generating apparatus according to claim 1 wherein the controller is arranged to further control the operation of the boiler in dependence upon a temperature or pressure signal from the sensor and stops the boiler heating water when the sensed temperature or pressure reaches a predetermined threshold value.
 9. A steam-generating apparatus according to claim 1 wherein the sensor comprises a thermistor mounted to a metallic substrate and the metallic substrate is mounted to the boiler.
 10. A method of operating a steam generating apparatus which comprises a water reservoir, a boiler for generating steam, a sensor connected to the boiler for detecting the temperature of or pressure in the boiler, a pump configured to pump water from the reservoir to the boiler, and a controller configured to receive a signal from the sensor and control operation of the pump in dependence on the signal, the method comprising determining an amount of water within the boiler and controlling the pump to supply water to the boiler when the determined amount of water is less than a predetermined value, wherein the method comprises determining the amount of water by measuring at least one time interval needed for a predetermined increases in temperature of or pressure in the boiler, and comparing the measured time interval with a predetermined value.
 11. A method according to claim 10 comprising measuring a time interval for an incremental increase in boiler temperature or pressure only when a control valve to allow steam to be released from the boiler is closed and steam is prevented from being released from the boiler.
 12. A method according to claim 11 comprising starting measurement of a time interval for an incremental increase in boiler temperature or pressure following closing of the control valve after steam has been released from the boiler, and after a predetermined time period has elapsed after closure of the control valve.
 13. A method according to claim 10 comprising operating the pump for a predetermined period of time in dependence upon the determined amount of water remaining in the boiler.
 14. A method according to claim 10 wherein the step of comparing the measured time interval with a predetermined value comprises comparing a measured time interval with a predetermined time interval for incremental temperature or pressure increases of one or more known amounts of water within the boiler stored in one or more look-up tables within a memory unit of the controller.
 15. A method according to claim 10 comprising controlling operation of the boiler in dependence upon a temperature or pressure signal from the sensor and stopping the boiler heating water when the sensed temperature or pressure reaches a predetermined threshold value. 